P0404 Exhaust Gas Recirculation Circuit Malfunction

You’re driving down the road, radio humming your favorite tune, when suddenly, your vehicle’s check engine light illuminates. An ominous sign, isn’t it?

You scan the vehicle and it throws the P0404 code. You’re now probably thinking, “What is this P0404 code? Is it serious?” We’re here to answer all your questions. Let’s unravel this mystery together.

What is P0404 Exhaust Gas Recirculation Circuit Malfunction?

Explanation of the Code

Simply put, the P0404 code is a standard OBD-II trouble code that indicates an issue with the Exhaust Gas Recirculation (EGR) Circuit. It signifies that the car’s computer, also known as the powertrain control module (PCM), has detected an issue with the EGR system’s performance or operation.

Role of Exhaust Gas Recirculation (EGR)

Ever wondered about the magic behind your car’s lower emissions and better fuel efficiency? That’s where the EGR system comes into play. Its main function is to reduce nitrogen oxide emissions, a significant contributor to air pollution, by recirculating a portion of your engine’s exhaust gases back into the engine cylinders.

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Symptoms of P0404 Malfunction

Identifying the P0404 code early on can save you a headache down the road. But how would you know? Here are some signs.

Power Loss

Does your vehicle struggle to accelerate as it used to? This could be due to the P0404 code. With a malfunctioning EGR system, the engine might fail to get the correct gas mixture, resulting in reduced power.

Fuel Efficiency Reduction

Seeing your fuel gauge drop quicker than usual? The EGR’s malfunction might be the culprit. A non-functional EGR can disrupt the engine’s fuel-air ratio, leading to excessive fuel consumption.

Poor Emission Test Results

Failed emission tests are another strong indicator. A faulty EGR system can increase nitrogen oxide emissions, leading to failed emission tests.

Possible Causes of P0404 Malfunction

Several factors can trigger this code. Some of them are:

Faulty EGR Valve

A damaged EGR valve can hinder the recirculation of exhaust gases, leading to the P0404 code.

EGR Passage Clogs

Over time, carbon deposits can clog the EGR passages, disrupting the flow of recirculated gases.

EGR Wiring or Connector Issues

Electrical issues such as damaged wiring or loose connectors may also trigger the P0404 code.

How to Diagnose P0404 Malfunction

Diagnosing the P0404 code might seem like a daunting task, but with a systematic approach, you can pinpoint the problem. Here’s how:

Preliminary Checks

Start by checking for any other trouble codes. The P0404 code often comes with other codes that can provide additional clues about the issue.

Manual Inspection of Components

Inspect the EGR valve, passages, and electrical connections. Look for visible damages, clogs, or loose connections.

Use of Diagnostic Tools

You may need to use a digital multimeter or a professional scan tool to perform advanced diagnostic tests.

How to Fix P0404 Malfunction

Armed with your diagnosis, it’s time to fix the issue. Here’s what you can do:

Cleaning the EGR Valve and Passages

Sometimes, all your EGR system needs is a good clean-up. Using a suitable cleaner, remove carbon deposits from the EGR valve and passages.

Replacing Faulty Components

If cleaning doesn’t work or if you find damaged components, replacement is the way to go. Make sure to replace them with high-quality parts for longevity.


The P0404 Exhaust Gas Recirculation Circuit Malfunction might seem like a mouthful, but once understood, it’s manageable. It is a signal for you to check your vehicle’s EGR system, ensuring a smoother drive, better fuel efficiency, and lower emissions.

Remember, early detection and appropriate action are key to maintaining your vehicle’s health.


Q1: Can I drive my car with a P0404 code?

A: It’s not recommended to drive your car extensively with this code as it can damage the engine over time.

Q2: How much does it cost to fix a P0404 code?

A: Depending on the exact issue and your car model, the cost can range from $100 to $400.

Q3: Can a faulty EGR valve affect fuel efficiency?

A: Yes, a malfunctioning EGR system can disrupt the fuel-air ratio, leading to higher fuel consumption.

Q4: How often should I clean the EGR valve?

A: There’s no set frequency, but a good rule of thumb is to check it every 50,000 miles.

Q5: Can I diagnose and fix a P0404 code myself?

A: Yes, with some automotive knowledge and the right tools, you can diagnose and even fix some issues related to the P0404 code.